Total and differential cross sections of η-production in proton–deuteron fusion for excess energies between Qη = 13 MeV and Qη = 81 MeV

Abstract New data on both total and differential cross sections of the production of η mesons in proton–deuteron fusion to He 3 η in the excess energy region 13.6 MeV ≤ Q η ≤ 80.9 MeV are presented. These data have been obtained with the WASA-at-COSY detector setup located at the Forschungszentrum Julich, using a proton beam at 15 different beam momenta between p p = 1.60 GeV / c and p p = 1.74 GeV / c . While significant structure of the total cross section is observed in the energy region 20 MeV ≲ Q η ≲ 60 MeV , a previously reported sharp variation around Q η ≈ 50 MeV cannot be confirmed. Angular distributions show the typical forward-peaking that was noted earlier. For the first time, it is possible to study the development of these angular distributions with rising excess energy over a wide interval.